Resist composition and patterning process

ABSTRACT

A polymer having a partial structure —C(CF 3 ) 2 OH in recurring units is used as an additive to formulate a resist composition. A photoresist film formed from the resist composition has sufficient barrier performance against water to prevent any resist components from being leached in water and thus minimize any change of pattern profile.

CROSS-REFERENCE TO RELATED APPLICATION

This non-provisional application claims priority under 35 U.S.C. §119(a)on Patent Application No. 2010-277875 filed in Japan on Dec. 14, 2010,the entire contents of which are hereby incorporated by reference.

TECHNICAL FIELD

This invention relates to a resist composition for use in aphotolithography process for the microfabrication of semiconductordevices, and particularly an immersion photolithography processinvolving directing ArF excimer laser radiation of wavelength 193 nmtoward a resist-coated substrate, with water held between a projectionlens and the substrate, and a process for forming a resist pattern.

BACKGROUND ART

In the recent drive for higher integration densities and operatingspeeds in LSI devices, the pattern rule is made drastically finer. Thebackground supporting such a rapid advance is a reduced wavelength ofthe light source for exposure. The change-over from i-line (365 nm) of amercury lamp to shorter wavelength KrF excimer laser (248 nm) enabledmass-scale production of dynamic random access memories (DRAM) with anintegration degree of 64 MB (processing feature size ≦0.25 μm). Toestablish the micropatterning technology necessary for the fabricationof DRAM with an integration degree of 256 MB and 1 GB or more, thelithography using ArF excimer laser (193 nm) is under activeinvestigation. The ArF excimer laser lithography, combined with a highNA lens (NA≧0.9), is considered to comply with 65-nm node devices. Forthe fabrication of next 45-nm node devices, the F₂ laser lithography of157 nm wavelength became a candidate. However, because of many problemsincluding a cost and a shortage of resist performance, the employment ofF₂ lithography was postponed. ArF immersion lithography was proposed asa substitute for the F₂ lithography (see Proc. SPIE Vol. 4690, xxix,2002).

In the ArF immersion lithography, the space between the projection lensand the wafer is filled with water and ArF excimer laser is irradiatedthrough the water. Since water has a refractive index of 1.44 at 193 nm,pattern formation is possible even using a lens with NA of 1.0 orgreater. The theoretically possible maximum NA is 1.44. The resolutionis improved by an increment of NA. A combination of a lens having NA ofat least 1.2 with ultra-high resolution technology suggests a way to the45-nm node (see Proc. SPIE Vol. 5040, p 724, 2003).

The ArF immersion lithography has a possibility that water-solublecomponents in the resist film be leached in immersion water duringexposure. Specifically an acid generated during exposure and a basiccompound previously added to the resist material can be leached inimmersion water. As a result, pattern profile changes and patterncollapse can occur. It is also pointed out that if the resist film isless water repellent, water droplets remaining on the resist film afterscanning, though in a minute volume, can penetrate into the resist filmto generate defects. It was then proposed to provide a protectivecoating between the resist film and water to prevent resist componentsfrom being leached out and water from penetrating into the resist film,the process being referred to as “topcoat process.” See 2nd ImmersionWorkshop: Resist and Cover Material Investigation for ImmersionLithography, 2003.

In the ArF immersion lithography using a topcoat, a protective coatingmaterial which is soluble in alkaline developer is advantageous. Thiseliminates the step of stripping off the protective coating, offeringgreat cost and process merits. Thus, great efforts have been devoted todevelop water-insoluble resist protective coating materials, forexample, resins having alkali-soluble units such as fluorinated alcohol,carboxyl or sulfo groups. See WO 2005/42453 and WO 2005/69676.

On the other hand, a process for preventing resist components from beingleached out and water from penetrating into the resist film without aneed for a protective coating material has also been developed, theprocess being referred to as “topcoatless process”. See JP-A 2006-48029,JP-A 2006-309245, and JP-A 2007-187887. In the topcoatless process, analkali-soluble hydrophobic polymer is added to the resist material as asurfactant, whereupon the hydrophobic compound is segregated at theresist surface during resist film formation. The process is thusexpected to achieve equivalent effects to the use of resist protectivecoating material. Additionally, the process is economically advantageousover the use of a resist protective film because steps of forming andremoving the protective film are unnecessary.

In either of the topcoat and topcoatless processes, the ArF immersionlithography requires a scanning speed of about 300 to 700 mm/sec inorder to gain higher throughputs. In the event of such high-speedscanning, if the water repellency of the resist or protective film isinsufficient, water droplets may be left on the film surface afterscanning. Residual droplets may cause defects. To eliminate suchdefects, it is necessary to improve the water repellency of the relevantcoating film and the flow or mobility of water (hereinafter, water slip)on the film. The film material must be designed so as to increase thereceding contact angle (see 2nd International Symposium on ImmersionLithography, 12-15 Sep. 2005, Defectivity data taken with a full-fieldimmersion exposure tool, Nakano et al). In connection with such polymerdesign, it is reported that introduction of fluorine is effective forimproving water repellency, and formation of micro-domain structure by acombination of different water repellent groups is effective forimproving water slip. See XXIV FATIPEC Congress Book, Vol. B, p 15(1997).

One exemplary material known to have excellent water slip and waterrepellency on film surface is a copolymer of α-trifluoromethylacrylateand norbornene derivative (Proc. SPIE Vol. 4690, p 18, 2002). While thispolymer was developed as the resin for F₂ (157 nm) lithography resistmaterials, it is characterized by a regular arrangement of molecules of(highly water repellent) α-trifluoromethylacrylate and norbornenederivative in a ratio of 2:1. When a water molecule interacts withmethyl and trifluoromethyl groups, there is a tendency that theorientation distance between water and methyl is longer. A resin havinga regular arrangement of both substituent groups is improved in waterslip because of a longer orientation distance of water. In fact, whenthis polymer is used as the base polymer in a protective coating forimmersion lithography, water slip is drastically improved (see US20070122736 or JP-A 2007-140446). Another example of the highly waterrepellent/water slippery material is a fluorinated ring-closingpolymerization polymer having hexafluoroalcohol groups on side chains.This polymer is further improved in water slip by protecting hydroxylgroups on side chains with acid labile groups, as reported in Proc. SPIEVol. 6519, p 651905 (2007).

Although the introduction of fluorine into resins is effective forimproving water repellency and water slip, the introduction of extrafluorine can induce new defects known as “blob defects”. Blob defectsare likely to form during spin drying after development, particularlywhen the film has a high surface contact angle after development. Oneapproach for suppressing blob defects is by introducing highlyhydrophilic substituent groups (e.g., carboxyl or sulfo groups) into aresin to reduce the surface contact angle after development. However,since these groups serve to reduce the water repellency and water slipof the resin, this approach is not applicable to high-speed scanning.There is a desire to have a material which can minimize blob defectswhile maintaining highly water repellent and water slip propertiesduring immersion lithography.

The highly water repellent/water slippery materials discussed above areexpected to be applied not only to the ArF immersion lithography, butalso to the resist material for mask blanks. Resist materials for maskblanks are subject to long-term exposure in vacuum. It is pointed outthat sensitivity variations or profile changes can occur as an aminecomponent in the resist material is adsorbed to the resist film surfaceduring the long-term exposure. It was then proposed to add a compoundhaving surface active effect to modify the surface of a resist film forpreventing adsorption of amine to the resist film.

CITATION LIST

-   Patent Document 1: WO 2005/42453-   Patent Document 2: WO 2005/69676-   Patent Document 3: JP-A 2006-048029-   Patent Document 4: JP-A 2006-309245-   Patent Document 5: JP-A 2007-187887-   Patent Document 6: US 20070122736 (JP-A 2007-140446)-   Non-Patent Document 1: Proc. SPIE Vol. 4690, xxix (2002)-   Non-Patent Document 2: Proc. SPIE Vol. 5040, p 724 (2003)-   Non-Patent Document 3: 2nd Immersion Workshop: Resist and Cover    Material Investigation for Immersion Lithography (2003)-   Non-Patent Document 4: 2nd International Symposium on Immersion    Lithography, 12-15 Sep. 2005, Defectivity data taken with a    full-field immersion exposure tool, Nakano et al.-   Non-Patent Document 5: XXIV FATIPEC Congress Book, Vol. B, p 15    (1997)-   Non-Patent Document 6: Proc. SPIE Vol. 4690, p 18 (2002)-   Non-Patent Document 7: Proc. SPIE Vol. 6519, p 651905 (2007)

SUMMARY OF INVENTION

An object of the invention is to provide a resist composition,especially chemically amplified positive resist composition comprisingan additive polymer, which composition exhibits water repellency, waterslip and minimal development defects, and a pattern forming processusing the composition. The additive polymer used herein is highlytransparent to radiation with wavelength of up to 200 nm. Variousproperties of the polymer including water repellency, water slip, fatsolubility, acid lability, and hydrolysis may be adjusted by a choice ofpolymer structure. The polymer can be prepared from reactants which arereadily available and easy to handle.

The inventors have found that when a polymer having a fluorinatedalcohol of specific structure, specifically a partial structure—C(CF₃)₂OH in recurring units is used as an additive to formulate aresist composition, the resist composition forms a resist film which hassufficient water repellency and water slip to withstand high-speedscanning without a need for a resist protective film.

Accordingly, the present invention provides a resist composition and apattern forming process, as defined below.

In a one aspect, the invention provides a resist composition comprising(A) a polymer comprising recurring units of the following generalformula (1a), (B) a polymer having a lactone ring-derived structure,hydroxyl-containing structure and/or maleic anhydride-derived structureand adapted to become soluble in an alkaline developer under the actionof an acid as a base resin, (C) a compound capable of generating an acidupon exposure to high-energy radiation, and (D) an organic solvent.

Herein R¹ is hydrogen or a straight, branched or cyclic C₁-C₂₀monovalent hydrocarbon group in which a constituent moiety —CH₂— may bereplaced by —O— or —C(═O)—, R² is hydrogen, fluorine, methyl ortrifluoromethyl, Aa is a straight, branched or cyclic C₁-C₂₀ hydrocarbonor fluorinated hydrocarbon group having a valence of k¹+1, Ab is astraight, branched or cyclic C₁-C₆ divalent hydrocarbon group, k¹ is aninteger of 1 to 3, and k² is 0 or 1.

In a preferred embodiment, the additive polymer (A) comprises recurringunits of formula (1a) and recurring units of one or more type selectedfrom the general formulae (2a) to (2j).

Herein R² is as defined above, R^(4a) and R^(4b) are each independentlyhydrogen or a straight, branched or cyclic monovalent hydrocarbon group,or R^(4a) and R^(4b) may bond together to form a non-aromatic ring of 3to 8 carbon atoms with the carbon atom to which they are attached,R^(5a) is hydrogen, a straight, branched or cyclic C₁-C₁₅ monovalenthydrocarbon or fluorinated hydrocarbon group, or an acid labile group,in the case of hydrocarbon group, a constituent moiety —CH₂— may bereplaced by —O— or —C(═O)—, R^(6a), R^(6b) and R^(6c) are eachindependently hydrogen, or a straight, branched or cyclic C₁-C₁₅monovalent hydrocarbon group, R^(6a) and R^(6b), R^(6a) and R^(6c), orR^(6b) and R^(6c) may bond together to form a non-aromatic ring of 3 to8 carbon atoms with the carbon atom to which they are attached, R^(7a)is hydrogen, or a straight, branched or cyclic C₁-C₁₅ monovalenthydrocarbon group, R^(7b) is a straight, branched or cyclic C₁-C₁₅monovalent hydrocarbon group, R^(7a) and R^(7b) may bond together toform a non-aromatic ring of 3 to 8 carbon atoms with the carbon atom towhich they are attached, R^(8a), R^(8b) and R^(8c) are eachindependently a straight, branched or cyclic C₁-C₁₅ monovalentfluorinated hydrocarbon group, R^(9a) is a straight, branched or cyclicC₁-C₁₅ monovalent hydrocarbon or fluorinated hydrocarbon group, and k²is 0 or 1.

In a preferred embodiment, the base polymer (B) is selected from thegroup consisting of (meth)acrylate polymers,(α-trifluoromethyl)acrylate-maleic anhydride copolymers,cycloolefin-maleic anhydride copolymers, polynorbornene, polymersresulting from ring-opening metathesis polymerization of cycloolefins,hydrogenated polymers resulting from ring-opening metathesispolymerization of cycloolefins, copolymers of hydroxystyrene with(meth)acrylate, styrene, vinylnaphthalene, vinylanthracene, vinylpyrene,hydroxyvinylnaphthalene, hydroxyvinylanthracene, indene, hydroxyindene,acenaphthylene, or norbornadiene derivatives, and novolac resins.

The base polymer (B) may comprise recurring units of at least one typeselected from the general formulae (2A) to (2D):

wherein R^(1A) is hydrogen, fluorine, methyl or trifluoromethyl, XA isan acid labile group, XB and XC are each independently a single bond ora straight or branched C₁-C₄ divalent hydrocarbon group, YA is asubstituent group having a lactone structure, ZA is hydrogen, a C₁-C₁₅fluoroalkyl group or C₁-C₁₅ fluoroalcohol-containing substituent group,and k^(1A) is an integer of 1 to 3.

In a preferred embodiment, the polymer (A) comprising recurring units offormula (1a) is added in an amount of 0.1 to 50 parts by weight per 100parts by weight of the polymer (B).

The resist composition may further comprise (E) a basic compound and/or(F) a dissolution regulator.

In another aspect, the invention provides:

a pattern forming process comprising the steps of (1) applying theresist composition defined above onto a substrate, (2) heat treating andexposing the resulting resist film to high-energy radiation through aphotomask, and (3) developing with a developer;

a pattern forming process comprising the steps of (1) applying theresist composition defined above onto a substrate, (2) heat treating andexposing the resulting resist film to high-energy radiation from aprojection lens through a photomask while holding a liquid between thesubstrate and the projection lens, and (3) developing with a developer;or

a pattern forming process comprising the steps of (1) applying theresist composition defined above onto a substrate to form a resist film,(2) forming a protective coating onto the resist film, (3) heat treatingand exposing the resist film to high-energy radiation from a projectionlens through a photomask while holding a liquid between the substrateand the projection lens, and (4) developing with a developer.

Typically, the liquid is water. The preferred high-energy radiation hasa wavelength in the range of 180 to 250 nm.

In a further aspect, the invention provides a pattern forming processcomprising the steps of (1) applying the resist composition definedabove onto a mask blank, (2) heat treating and exposing the resultingresist film in vacuum to electron beam, and (3) developing with adeveloper.

Advantageous Effects of Invention

A photoresist film formed from the resist composition of the inventionhas sufficient barrier performance against water to prevent any resistcomponents from being leached in water and thus minimize any change ofpattern profile due to leach-out. Absent a need for a protective filmwhich is commonly formed in the immersion lithography to preventleach-out, the invention saves the cost for protective film formation.

The photoresist film has a high receding contact angle with water,allows few water droplets to be left on the photoresist film surfaceafter scanning in the immersion lithography process, and thus minimizesa pattern formation failure caused by residual droplets on the filmsurface. The use of the resist composition according to the inventionreduces the cost of the immersion lithography process and enablesformation of a fine size pattern with few defects at a high accuracy.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a SEM image showing a bridge defect on a resist pattern.

FIG. 2 is a SEM image showing a watermark defect on a resist pattern.

DESCRIPTION OF EMBODIMENTS

The singular forms “a”, “an” and “the” include plural referents unlessthe context clearly dictates otherwise. The notation (Cn-Cm) means agroup containing from n to m carbon atoms per group. The abbreviationPAG stands for photoacid generator, PEB for post-exposure bake, EB forelectron beam, EUV for extreme ultraviolet. The abbreviation “phr” isparts by weight per 100 parts by weight of the base resin.

While a certain compound is herein represented by a chemical formula,many compounds have a chemical structure for which there can existenantiomers or diastereomers. Each chemical formula collectivelyrepresents all such stereoisomers, unless otherwise stated. Suchstereoisomers may be used alone or in admixture.

Additive Polymer

The polymer used as an additive in the resist composition of theinvention is characterized by comprising recurring units having thegeneral formula (1a). For convenience of description, the polymercomprising recurring units of formula (1a) is referred to as “polymerP1,” hereinafter.

Herein R¹ is hydrogen or a straight, branched or cyclic C₁-C₂₀,monovalent hydrocarbon group in which a constituent moiety —CH₁— may bereplaced by —O— or —C(═O)—, R² is hydrogen, fluorine, methyl ortrifluoromethyl, Aa is a straight, branched or cyclic C₁-C₂₀ hydrocarbonor fluorinated hydrocarbon group having a valence of k¹+1, Ab is astraight, branched or cyclic C₁-C₂₀ divalent hydrocarbon group, k¹ is aninteger of 1 to 3, and k² is 0 or 1.

Polymer P1 is characterized in that the recurring units of formula (1a)each contain a plurality of fluorine atoms. Once polymer P1 is added toa resist composition, polymer P1 itself functions as a surfactant toprovide a distribution at the time when a resist film is formed, thatpolymer P1 is segregated at the resist film surface.

In general, fluorinated polymers exert excellent functions of waterrepellency and water slip. When polymer P1 is used as a resist additive,it is possible to form a resist film having a surface exerting excellentwater repellency and water slip at the same time as its formation. Aneffect equivalent to the use of resist protective coating material isexpectable. This approach is also advantageous in cost because iteliminates the steps of forming and removing a resist protectivecoating.

In formula (1a), the monovalent hydrocarbon groups represented by R¹include groups for protecting an alcoholic hydroxyl group, specificallygroups having the general formula (R1-1) and (R1-2), tertiary alkylgroups of 4 to 15 carbon atoms, trialkylsilyl groups in which each alkylmoiety has 1 to 5 carbon atoms, oxoalkyl groups of 4 to 15 carbon atoms,and acyl groups of 1 to 10 carbon atoms.

Herein and throughout the specification, the broken line designates avalence bond. R^(L01) and R^(L02) each independently hydrogen or astraight, branched or cyclic alkyl group of 1 to 18 carbon atoms,preferably 1 to 10 carbon atoms. Examples include methyl, ethyl, propyl,isopropyl, n-butyl, sec-butyl, tert-butyl, cyclopentyl, cyclohexyl,2-ethylhexyl, n-octyl, norbornyl, tricyclodecanyl, tetracyclododecanyl,and adamantyl. R^(L03) is a monovalent hydrocarbon group of 1 to 18carbon atoms, preferably 1 to 10 carbon atoms, which may contain aheteroatom such as oxygen, examples of which include straight, branchedor cyclic alkyl groups and substituted forms of such alkyl groups inwhich some hydrogen atoms are replaced by hydroxyl, alkoxy, oxo, amino,alkylamino or the like. Examples of the substituted alkyl groups are asshown below.

A pair of R^(L01) and R^(L02), R^(L01) and R^(L03), or R^(L02) andR^(L03) may bond together to form a ring with carbon and oxygen atoms towhich they are attached. Each of ring-forming R^(L01), R^(L02) andR^(L03) is a straight or branched alkylene group of 1 to 18 carbonatoms, preferably 1 to 10 carbon atoms when they form a ring.

In formula (R1-2), R^(L04) is a tertiary alkyl group of 4 to 20 carbonatoms, preferably 4 to 15 carbon atoms, a trialkylsilyl group in whicheach alkyl moiety has 1 to 6 carbon atoms, an oxoalkyl group of 4 to 20carbon atoms, or a group of formula (R1-1). The subscript y is aninteger of 0 to 6.

Suitable groups of R¹ and R^(L04) are illustrated below. Exemplarytertiary alkyl groups include tert-butyl, tert-amyl, 1,1-diethylpropyl,2-cyclopentylpropan-2-yl, 2-cyclohexylpropan-2-yl,2-(bicyclo[2.2.1]heptan-2-yl)propan-2-yl, 2-(adamantan-1-yl)propan-2-yl,1-ethylcyclopentyl, 1-butylcyclopentyl, 1-ethylcyclohexyl,1-butylcyclohexyl, 1-ethyl-2-cyclopentenyl, 1-ethyl-2-cyclohexenyl,2-methyl-2-adamantyl, 2-ethyl-2-adamantyl, and the like. Exemplarytrialkylsilyl groups are trimethylsilyl, triethylsilyl, anddimethyl-tert-butylsilyl. Exemplary oxoalkyl groups are 3-oxocyclohexyl,4-methyl-2-oxooxan-4-yl, and 5-methyl-2-oxooxolan-5-yl. Examples of theacyl group include formyl, acetyl, ethylcarbonyl, pivaloyl,methoxycarbonyl, ethoxycarbonyl, tert-butoxycarbonyl, trifluoroacetyl,and trichloroacetyl.

Of the protective groups of formula (R1-1), the straight or branchedgroups are exemplified by the following.

Of the protective groups of formula (R1-1), the cyclic ones are, forexample, tetrahydrofuran-2-yl, 2-methyltetrahydrofuran-2-yl,tetrahydropyran-2-yl, and 2-methyltetrahydropyran-2-yl.

Examples of the protective groups of formula (R1-2) includetert-butoxycarbonyl, tert-butoxycarbonylmethyl, tert-amyloxycarbonyl,tert-amyloxycarbonylmethyl, 1,1-diethylpropyloxycarbonyl,1,1-diethylpropyloxycarbonylmethyl, 1-ethylcyclopentyloxycarbonyl,1-ethylcyclopentyloxycarbonylmethyl, 1-ethyl-2-cyclopentenyloxycarbonyl,1-ethyl-2-cyclopentenyloxycarbonylmethyl, 1-ethoxyethoxycarbonylmethyl,2-tetrahydropyranyloxycarbonylmethyl, and2-tetrahydrofuranyloxycarbonylmethyl.

Referring back to formula (1a), Aa is a straight, branched or cyclicC₁-C₂₀ hydrocarbon or fluorinated hydrocarbon group having a valence ofk¹+1. Examples of the C₁-C₂₀ hydrocarbon group are shown below.

Examples of the C₁-C₂₀ fluorinated hydrocarbon group include fluorinatedforms of the foregoing in which some or all hydrogen atoms are replacedby fluorine atoms.

Ab is a straight, branched or cyclic C₁-C₆ divalent hydrocarbon group,examples of which are shown below.

Illustrative, non-limiting examples of the recurring units havingformula (1a) are shown below.

Herein R² is as defined above, and Me is methyl.

In addition to the recurring units of formula (1a), the additive polymerP1 may further comprise recurring units of one or multiple typesselected from the general formulae (2a) to (2j). The polymer havingadditional recurring units incorporated herein is more improved in waterrepellency, water slip, alkaline dissolution, and contact angle afterdevelopment.

Herein R² is as defined above. R^(4a) and R^(4b) are each independentlyhydrogen or a straight, branched or cyclic C₁-C₁₅ monovalent hydrocarbongroup, or R^(4a) and R^(4b) may bond together to form a C₃-C₈non-aromatic ring with the carbon atom to which they are attached.R^(5a) is hydrogen, a straight, branched or cyclic C₁-C₁₅ monovalenthydrocarbon or fluorinated hydrocarbon group, or an acid labile group.In the case of monovalent hydrocarbon group, a constituent moiety —CH₁—may be replaced by —O— or —C(═O)—. R^(6a), R^(6b) and R^(6c) are eachindependently hydrogen or a straight, branched or cyclic C₁-C₁₅monovalent hydrocarbon group, or R^(6a) and R^(6b), R^(6a) and R^(6c),or R^(6b) and R^(6c) may bond together to form a C₃-C₈ non-aromatic ringwith the carbon atom to which they are attached. R^(7a) is hydrogen or astraight, branched or cyclic C₁-C₁₅ monovalent hydrocarbon group, R^(7b)is a straight, branched or cyclic C₁-C₁₅ monovalent hydrocarbon group,or R^(7a) and R^(7b) may bond together to form a C₃-C₈ non-aromatic ringwith the carbon atom to which they are attached. R^(8a), R^(8b), andR^(8c) are each independently a straight, branched or cyclic C₁-C₁₅monovalent fluorinated hydrocarbon group. R^(9a) is a straight, branchedor cyclic C₁-C₁₅ monovalent hydrocarbon or fluorinated hydrocarbongroup. The subscript k² is 0 or 1.

With respect to R^(4a), R^(4b), R^(5a), R^(6a), R^(6b), R^(6c), R^(7a),R^(7b), and R^(9a), suitable straight, branched or cyclic alkyl groupsinclude methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl,tert-butyl, tert-amyl, n-pentyl, n-hexyl, n-heptyl, n-octyl, n-nonyl,n-decyl, cyclopentyl, cyclohexyl, cyclopentylmethyl, cyclopentylethyl,cyclopentylbutyl, cyclohexylmethyl, cyclohexylethyl, cyclohexylbutyl,and adamantyl. A pair of R^(4a) and R^(4b), R^(6a) and R^(6b), R^(6a)and R^(6c), R^(6b) and R^(6c), or R^(7a) and R^(7b) may bond together toform a C₃-C₈ non-aromatic ring with the carbon atom to which they areattached. In the event of cyclization, each R is an alkylene groupcorresponding to the foregoing alkyl groups with one hydrogen atomeliminated therefrom, and exemplary rings are cyclopentyl andcyclohexyl.

R^(5a), R^(8a), R^(8b), R^(8c), and R^(9a) stand for straight, branchedor cyclic C₁-C₁₅ monovalent fluorinated hydrocarbon groups, specificallyfluoroalkyl groups which are typically substituted forms of theforegoing alkyl groups in which some or all hydrogen atoms aresubstituted by fluorine atoms. Examples include, but are not limited to,trifluoromethyl, 2,2,2-trifluoroethyl, 3,3,3-trifluoro-1-propyl,3,3,3-trifluoro-2-propyl, 2,2,3,3-tetrafluoropropyl,1,1,1,3,3,3-hexafluoroisopropyl, 2,2,3,3,4,4,4-heptafluorobutyl,2,2,3,3,4,4,5,5-octafluoropentyl,2,2,3,3,4,4,5,5,6,6,7,7-dodecafluoroheptyl, 2-(perfluorobutyl)ethyl,2-(perfluorohexyl)ethyl, 2-(perfluorooctyl)ethyl,2-(perfluorodecyl)ethyl, and 3,3,4,4,5,5,6,6,6-nonafluorohexyl. Examplesof the straight, branched or cyclic fluoroalkyl group represented byR^(8a) include trifluoromethyl, 2,2,2-trifluoroethyl,3,3,3-trifluoro-1-propyl, 3,3,3-trifluoro-2-propyl,2,2,3,3-tetrafluoropropyl, 1,1,1,3,3,3-hexafluoroisopropyl,2,2,3,3,4,4,4-heptafluorobutyl, 2,2,3,3,4,4,5,5-octafluoropentyl,2,2,3,3,4,4,5,5,6,6,7,7-dodecafluoroheptyl, 2-(perfluorobutyl)ethyl,2-(perfluorohexyl)ethyl, 2-(perfluorooctyl)ethyl, and3,3,4,4,5,5,6,6,6-nonafluorohexyl.

The acid labile group represented by R^(5a) may be selected from avariety of such groups. Examples of the acid labile group are groups ofthe following general formulae (L1) to (L4), tertiary alkyl groups of 4to 20 carbon atoms, preferably 4 to 15 carbon atoms, trialkylsilylgroups in which each alkyl moiety has 1 to 6 carbon atoms, and oxoalkylgroups of 4 to 20 carbon atoms.

Herein R^(L01) and R^(L02) are each independently hydrogen or astraight, branched or cyclic alkyl group of 1 to 18 carbon atoms,preferably 1 to 10 carbon atoms. R^(L03) is a monovalent hydrocarbongroup of 1 to 18 carbon atoms, preferably 1 to 10 carbon atoms, whichmay contain a heteroatom such as oxygen, examples of which includestraight, branched or cyclic alkyl groups and substituted forms of suchalkyl groups in which some hydrogen atoms are replaced by hydroxyl,alkoxy, oxo, amino, alkylamino or the like. R^(L04) is a tertiary alkylgroup of 4 to 20 carbon atoms, preferably 4 to 15 carbon atoms, atrialkylsilyl group in which each alkyl moiety has 1 to 6 carbon atoms,an oxoalkyl group of 4 to 20 carbon atoms, or a group of formula (L1).R^(L05) is an optionally substituted, straight, branched or cyclicC₁-C₁₀ alkyl group or an optionally substituted C₆-C₂₀ aryl group.R^(L06) is an optionally substituted, straight, branched or cyclicC₁-C₁₀ alkyl group or an optionally substituted C₆-C₂₀ aryl group.R^(L07) to R^(L16) independently represent hydrogen or optionallysubstituted monovalent hydrocarbon groups of 1 to 15 carbon atoms.Letter y is an integer of 0 to 6, m is equal to 0 or 1, n is equal to 0,1, 2 or 3, and 2 m+n is equal to 2 or 3. The broken line denotes avalence bond.

In formula (L1), exemplary groups of R^(L01) and R^(L02) include methyl,ethyl, propyl, isopropyl, n-butyl, sec-butyl, tert-butyl, cyclopentyl,cyclohexyl, 2-ethylhexyl, n-octyl, and adamantyl. R^(L03) is amonovalent hydrocarbon group of 1 to 18 carbon atoms, preferably 1 to 10carbon atoms, which may contain a heteroatom such as oxygen, examples ofwhich include straight, branched or cyclic alkyl groups and substitutedforms of such alkyl groups in which some hydrogen atoms are replaced byhydroxyl, alkoxy, oxo, amino, alkylamino or the like. Illustrativeexamples of the straight, branched or cyclic alkyl groups are asexemplified above for R^(L01) and R^(L02), and examples of thesubstituted alkyl groups are as shown below.

A pair of R^(L01) and R^(L02), R^(L01) and R^(L03), or R^(L02) andR^(L03) may bond together to form a ring with carbon and oxygen atoms towhich they are attached. Each of ring-forming R^(L01), R^(L02) andR^(L03) is a straight or branched alkylene group of 1 to 18 carbonatoms, preferably 1 to 10 carbon atoms when they form a ring.

In formula (L2), exemplary tertiary alkyl groups of R^(L04) aretert-butyl, tert-amyl, 1,1-diethylpropyl, 2-cyclopentylpropan-2-yl,2-cyclohexylpropan-2-yl, 2-(bicyclo[2.2.1]heptan-2-yl)propan-2-yl,2-(adamantan-1-yl)propan-2-yl, 1-ethylcyclopentyl, 1-butylcyclopentyl,1-ethylcyclohexyl, 1-butylcyclohexyl, 1-ethyl-2-cyclopentenyl,1-ethyl-2-cyclohexenyl, 2-methyl-2-adamantyl, 2-ethyl-2-adamantyl, andthe like. Exemplary trialkylsilyl groups are trimethylsilyl,triethylsilyl, and dimethyl-tert-butylsilyl. Exemplary oxoalkyl groupsare 3-oxocyclohexyl, 4-methyl-2-oxooxan-4-yl, and5-methyl-2-oxooxolan-5-yl.

In formula (L3), examples of the optionally substituted C₁-C₁₀ alkylgroups of R^(L05) include straight, branched or cyclic alkyl groups suchas methyl, ethyl, propyl, isopropyl, n-butyl, sec-butyl, tert-butyl,tert-amyl, n-pentyl, n-hexyl, cyclopentyl, cyclohexyl, andbicyclo[2.2.1]heptyl, and substituted forms of such groups in which somehydrogen atoms are replaced by hydroxyl, alkoxy, carboxyl,alkoxycarbonyl, oxo, amino, alkylamino, cyano, mercapto, alkylthio,sulfo or other groups or in which a methylene moiety is replaced by anoxygen or sulfur atom. Examples of optionally substituted C₆-C₂₀ groupsinclude phenyl, methylphenyl, naphthyl, anthryl, phenanthryl, andpyrenyl.

In formula (L4), examples of optionally substituted, straight, branchedor cyclic C₁-C₁₀ alkyl groups and optionally substituted C₆-C₂₀ arylgroups of R^(L06) are the same as exemplified for R^(L05). ExemplaryC₁-C₁₅ monovalent hydrocarbon groups of R^(L07) to R^(L16) includestraight, branched or cyclic alkyl groups such as methyl, ethyl, propyl,isopropyl, n-butyl, sec-butyl, tert-butyl, tert-amyl, n-pentyl, n-hexyl,n-octyl, n-nonyl, n-decyl, cyclopentyl, cyclohexyl, cyclopentylmethyl,cyclopentylethyl, cyclopentylbutyl, cyclohexylmethyl, cyclohexylethyland cyclohexylbutyl, and substituted forms of these groups in which somehydrogen atoms are replaced by hydroxyl, alkoxy, carboxyl,alkoxycarbonyl, oxo, amino, alkylamino, cyano, mercapto, alkylthio,sulfo or other groups. Alternatively, two of R^(L07) to R^(L16) may bondtogether to form a non-aromatic ring with the carbon atom(s) to whichthey are attached (for example, a pair of R^(L07) and R^(L08), R^(L07)and R^(L09), R^(L07) and R^(L10), R^(L08) and R^(L10), R^(L09) andR^(L10), R^(L11) and R^(L12), or R^(L13) and R^(L14) form a ring). Eachof R^(L07) to R^(L16) represents a C₁-C₁₅ divalent hydrocarbon group,typically alkylene, when they form a ring, examples of which are thoseexemplified above for the monovalent hydrocarbon groups, with onehydrogen atom being eliminated. Two of R^(L07) to R^(L16) which areattached to vicinal carbon atoms may bond together directly to form adouble bond (for example, a pair of R^(L07) and R^(L09), R^(L09) andR^(L15), R^(L13) and R^(L15), or R^(L14) and R^(L15)).

Of the acid labile groups of formula (L1), the straight and branchedones are exemplified by the following groups.

Of the acid labile groups of formula (L1), the cyclic ones are, forexample, tetrahydrofuran-2-yl, 2-methyltetrahydrofuran-2-yl,tetrahydropyran-2-yl, and 2-methyltetrahydropyran-2-yl.

Examples of the acid labile groups of formula (L2) includetert-butoxycarbonyl, tert-butoxycarbonylmethyl, tert-amyloxycarbonyl,tert-amyloxycarbonylmethyl, 1,1-diethylpropyloxycarbonyl,1,1-diethylpropyloxycarbonylmethyl, 1-ethylcyclopentyloxycarbonyl,1-ethylcyclopentyloxycarbonylmethyl, 1-ethyl-2-cyclopentenyloxycarbonyl,1-ethyl-2-cyclopentenyloxycarbonylmethyl, 1-ethoxyethoxycarbonylmethyl,2-tetrahydropyranyloxycarbonylmethyl, and2-tetrahydrofuranyloxycarbonylmethyl.

Examples of the acid labile groups of formula (L3) include1-methylcyclopentyl, 1-ethylcyclopentyl, 1-n-propylcyclopentyl,1-isopropylcyclopentyl, 1-n-butylcyclopentyl, 1-sec-butylcyclopentyl,1-cyclohexylcyclopentyl, 1-(4-methoxy-n-butyl)cyclopentyl,1-(bicyclo[2.2.1]heptan-2-yl)cyclopentyl,1-(7-oxabicyclo[2.2.1]heptan-2-yl)cyclopentyl, 1-methylcyclohexyl,1-ethylcyclohexyl, 3-methyl-1-cyclopenten-3-yl,3-ethyl-1-cyclopenten-3-yl, 3-methyl-1-cyclohexen-3-yl, and3-ethyl-1-cyclohexen-3-yl.

Of the acid labile groups of formula (L4), those groups of the followingformulae (L4-1) to (L4-4) are preferred.

In formulas (L4-1) to (L4-4), the broken line denotes a bonding site anddirection. R^(L41) is each independently a monovalent hydrocarbon group,typically a straight, branched or cyclic C₁-C₁₀ alkyl group, such asmethyl, ethyl, propyl, isopropyl, n-butyl, sec-butyl, tert-butyl,tert-amyl, n-pentyl, n-hexyl, cyclopentyl and cyclohexyl.

For formulas (L4-1) to (L4-4), there can exist enantiomers anddiastereomers. Each of formulae (L4-1) to (L4-4) collectively representsall such stereoisomers. Such stereoisomers may be used alone or inadmixture.

For example, the general formula (L4-3) represents one or a mixture oftwo selected from groups having the following general formulas (L4-3-1)and (L4-3-2).

Note that R^(L41) is as defined above.

Similarly, the general formula (L4-4) represents one or a mixture of twoor more selected from groups having the following general formulas(L4-4-1) to (L4-4-4).

Note that R^(L41) is as defined above.

Each of formulas (L4-1) to (L4-4), (L4-3-1) and (L4-3-2), and (L4-4-1)to (L4-4-4) collectively represents an enantiomer thereof and a mixtureof enantiomers.

It is noted that in the above formulas (L4-1) to (L4-4), (L4-3-1) and(L4-3-2), and (L4-4-1) to (L4-4-4), the bond direction is on the exoside relative to the bicyclo[2.2.1]heptane ring, which ensures highreactivity for acid catalyzed elimination reaction (see JP-A2000-336121). In preparing these monomers having a tertiary exo-alkylgroup of bicyclo[2.2.1]heptane structure as a substituent group, theremay be contained monomers substituted with an endo-alkyl group asrepresented by the following formulas (L4-1-endo) to (L4-4-endo). Forgood reactivity, an exo proportion of at least 50 mol % is preferred,with an exo proportion of at least 80 mol % being more preferred.

Note that R^(L41) is as defined above.

Illustrative examples of the acid labile group of formula (L4) are givenbelow.

Examples of the tertiary C₄-C₂₀ alkyl groups, trialkylsilyl groups inwhich each alkyl moiety has 1 to 6 carbon atoms, and C₄-C₂₀ oxoalkylgroups, represented by R^(5a), are as exemplified for R^(L04) and thelike.

Illustrative examples of the recurring units having formulae (2a) to(2j) are given below, but not limited thereto.

Note that R² is as defined above.

Although the polymer P1 comprising recurring units of formula (1a) incombination with recurring units of formulae (2a) to (2j) exertssatisfactory performance as the resist additive, recurring units of oneor multiple types selected from formulae (3a) to (3e), (4a) to (4e),(5a) to (5c), and (6a) to (6c) may be further incorporated therein forthe purposes of imparting further water repellency and water slip, andcontrolling alkaline solubility and developer affinity.

Herein R¹¹ is a C₁-C₁₅ monovalent hydrocarbon or fluorinated hydrocarbongroup, R¹² is an adhesive group, R¹³ is an acid labile group, R¹⁴ is asingle bond or divalent C₁-C₁₅ organic group, and R¹⁵ and R¹⁶ each arehydrogen, methyl or trifluoromethyl.

Examples of the C₁-C₁₅ monovalent hydrocarbon and fluorinatedhydrocarbon groups represented by R¹¹ are the same as R^(5a) and R^(8a).

The adhesive group represented by R¹² may be selected from a variety ofsuch groups, typically those groups shown below.

Herein, the broken line designates a valence bond.

The acid labile group represented by R¹³ may be selected from thosegroups illustrated for R.

Suitable divalent C₁-C₁₅ organic groups represented by R¹⁴ include theabove-exemplified monovalent hydrocarbon groups, with one hydrogen atomeliminated (e.g., methylene and ethylene). Also useful are groups of thefollowing formulae.

Herein, the broken line designates a valence bond.Monomer Synthesis

The polymer P1 used as the additive in the resist composition ischaracterized by comprising essentially recurring units having formula(1a). Monomers from which these recurring units are derived may besynthesized by any well-known methods, for example, the method of JPAppln. 2010-218249.

Polymer Synthesis

The polymer P1 may be synthesized by general polymerization processesincluding radical polymerization using initiators such as2,2′-azobisisobutyronitrile (AIBN), and ionic (or anionic)polymerization using alkyl lithium or the like. The polymerization maybe carried out by its standard technique. Preferably the polymer P1 issynthesized by radical polymerization while the polymerizationconditions may be determined in accordance with the type and amount ofinitiator, temperature, pressure, concentration, solvent, additives, andthe like.

Examples of the radical polymerization initiator used herein include azocompounds such as 2,2′-azobisisobutyronitrile (AIBN),2,2′-azobis(4-methoxy-2,4-dimethylvaleronitrile),2,2′-azobis(2,4-dimethylvaleronitrile),2,2′-azobis(2,4,4-trimethylpentane), and dimethyl2,2′-azobis(isobutyrate); peroxides such as tert-butylperoxypivalate,lauroyl peroxide, benzoyl peroxide, and tert-butylperoxylaurate;water-soluble polymerization initiators such as potassium persulfate;and redox initiators comprising a peroxide (e.g., potassium persulfateor hydrogen peroxide) combined with a reducing agent (e.g., sodiumsulfite). Although the amount of polymerization initiator used may varywith its type and other polymerization conditions, it is generally usedin an amount of 0.001 to 10 mol %, and preferably 0.01 to 6 mol % basedon the total moles of monomers to be polymerized.

During the synthesis of polymer P1, any known chain transfer agent suchas dodecyl mercaptan or 2-mercaptoethanol may be added for molecularweight control purpose. The amount of chain transfer agent added ispreferably 0.01 to 10 mol % based on the total moles of monomers to bepolymerized.

Polymer P1 may be synthesized by combining suitable monomers selectedfrom polymerizable monomers corresponding to recurring units of formulae(1a), (2a) to (2j), (3a) to (3e), (4a) to (4e), (5a) to (5c), and (6a)to (6c), adding an initiator and chain transfer agent to the monomermixture, and effecting polymerization.

In polymer P1 wherein U1 stands for a total molar number of a monomercorresponding to units of formula (1a), U2 stands for a total molarnumber of monomers corresponding to units of formulae (2a) to (2j), andU3 stands for a total molar number of monomers corresponding to units offormulae (3a) to (3e), (4a) to (4e), (5a) to (5c), and (6a) to (6c),with the proviso that U1+U2+U3=U (=100 mol %), values of U1, U2, and U3are preferably determined so as to meet:

0≦U1/U<1, more preferably 0.1≦U1/U≦0.8, even more preferably0.1≦U1/U≦0.7,

0≦U2/U<1, more preferably 0.2≦U2/U≦0.9, even more preferably0.3≦U2/U≦0.9, and

0≦U3/U<1, more preferably 0≦U3/U≦0.4, even more preferably 0≦U3/U≦0.2.

For polymerization, a solvent may be used if desired. Preferred is thesolvent which does not interfere with the desired polymerizationreaction. Typical solvents used herein include esters such as ethylacetate, n-butyl acetate, and γ-butyrolactone; ketones such as acetone,methyl ethyl ketone, and methyl isobutyl ketone; aliphatic or aromatichydrocarbons such as toluene, xylene and cyclohexane; alcohols such asisopropyl alcohol and ethylene glycol monomethyl ether; and ethersolvents such as diethyl ether, dioxane, and tetrahydrofuran, which maybe used alone or in admixture. Although the amount of solvent used mayvary with the desired degree of polymerization (or molecular weight),the amount of initiator added, and other polymerization conditions suchas temperature, it is generally used in such an amount as to provide aconcentration of 0.1 to 95% by weight, preferably 5 to 90% by weight ofmonomers to be polymerized.

Although the temperature of the polymerization reaction may vary withthe identity of polymerization initiator or the boiling point ofsolvent, it is preferably in the range of 20 to 200° C., and morepreferably 50 to 140° C. Any desired reactor or vessel may be used forthe polymerization reaction.

From the solution or dispersion of the polymer thus synthesized, theorganic solvent or water serving as the reaction medium is removed byany well-known techniques. Suitable techniques include, for example,re-precipitation followed by filtration, and heat distillation undervacuum.

Desirably polymer P1 has a weight average molecular weight (Mw) of 1,000to 500,000, and especially 2,000 to 30,000, as determined versuspolystyrene standards by gel permeation chromatography (GPC) usingtetrahydrofuran as solvent. This is because a polymer with too low a Mwmay readily dissolve in water whereas too high a Mw may lead to adecline of alkali solubility and cause defect formation during spincoating.

In polymer P1, R¹ in formula (1a), R^(5a) in formulae (2a), (2b) and(2f), and R¹³ in formulae (3c) and (4c) may be introduced bypost-protection reaction. Specifically, a monomer wherein R¹, R^(5a) orR¹³ is hydrogen is previously polymerized to synthesize a precursorpolymer. Post-protection reaction is effected on the precursor polymerfor substituting groups R¹, R^(5a) or R¹³ for some or all hydroxylgroups on the precursor polymer as shown below.

Herein R¹, R^(5a), and R¹³ are as defined above, and X is chlorine,bromine or iodine.

The desired polymer is obtainable via post-protection reaction byreacting the precursor polymer with a base in an amount of 1 to 2equivalents relative to the desired degree of substitution of hydroxylgroups, and then with R¹—X, R^(5a)—X or R¹³—X in an amount of 1 to 2equivalents relative to the base.

The post-protection reaction may be effected in a solvent, which isselected from hydrocarbons such as benzene and toluene, and ethers suchas dibutyl ether, diethylene glycol diethyl ether, diethylene glycoldimethyl ether, tetrahydrofuran and 1,4-dioxane, alone or in admixture.Suitable bases used herein include, but are not limited to, sodiumhydride, n-butyl lithium, lithium diisopropylamide, triethylamine, andpyridine.

Resist Composition

Briefly stated, the resist composition is defined as comprising (A)polymer P1, in combination with (B) a base resin, i.e., polymer whichbecomes soluble in an alkaline developer under the action of an acid asa base resin. Since polymer P1 contains a plurality of fluorine atoms,the overall polymer functions as a surfactant. When a resist film isformed by spin coating the composition, polymer P1 segregates in asub-surface layer of the resist film. The sub-surface layer improves thewater repellency and water slip on the resist surface, and prevents anywater-soluble components in the resist composition from being leachedout.

Polymer P1 is added as an additive to the resist composition preferablyin an amount (total amount if plural polymers P1 are used) of 0.1 to 50parts, more preferably 0.5 to 10 parts by weight per 100 parts by weightof the base resin (B). At least 0.1 phr of polymer P1 is effective inimproving the receding contact angle with water of photoresist filmsurface, whereas up to 50 phr of polymer P1 forms a photoresist filmhaving a low dissolution rate in alkaline developer and capable ofmaintaining the height of a fine pattern formed therein.

Base Resin

The resist composition contains (B) a polymer having a lactonering-derived structure, hydroxyl-containing structure and/or maleicanhydride-derived structure and adapted to become soluble in an alkalinedeveloper under the action of an acid as a base resin. Examples of thebase polymer (B) include, but are not limited to, (meth)acrylatepolymers, (α-trifluoromethyl)acrylate-maleic anhydride copolymers,cycloolefin-maleic anhydride copolymers, polynorbornene, polymersresulting from ring-opening metathesis polymerization (ROMP) ofcycloolefins, hydrogenated cycloolefin ROMP polymers, copolymers ofhydroxystyrene with (meth)acrylate, styrene, vinylnaphthalene,vinylanthracene, vinylpyrene, hydroxyvinylnaphthalene,hydroxyvinylanthracene, indene, hydroxyindene, acenaphthylene, ornorbornadiene derivatives, and novolac resins. Examples of thesepolymers are described in U.S. Pat. No. 7,537,880 (JP-A 2008-111103,paragraph [0072] to [0120]). The polymer serving as base resin (B) isnot limited to one type and a mixture of two or more polymers may beadded. The use of plural polymers allows for easy adjustment of resistproperties.

The base polymer (B) may further comprise recurring units of at leastone type selected from the general formulae (2A) to (2D).

Herein R^(1A) is hydrogen, fluorine, methyl or trifluoromethyl, XA is anacid labile group, XB and XC are each independently a single bond or astraight or branched C₁-C₄ divalent hydrocarbon group (typicallyalkylene), YA is a substituent group having a lactone structure, ZA ishydrogen, or a C₁-C₁₅ fluoroalkyl group or C₁-C₁₅fluoroalcohol-containing substituent group, and k^(1A) is an integer of1 to 3.

A polymer comprising recurring units of formula (2A) is decomposed underthe action of an acid to generate carboxylic acid so that the polymermay become alkali soluble. While the acid labile group XA may beselected from a variety of such groups, it may be as exemplified abovefor R^(5a) in formulae (2a) to (2j).

Examples of recurring units of formula (2A) are given below, but notlimited thereto.

Examples of recurring units of formula (2B) are given below, but notlimited thereto.

Examples of recurring units of formula (2C) are given below, but notlimited thereto.

Examples of recurring units of formula (2D) are given below, but notlimited thereto.

The base polymer (B) may have further copolymerized therein any ofsulfonium salts (f1) to (f3) represented by the following generalformulae.

Herein R²⁰, R²⁴ and R²⁸ each are hydrogen or methyl. R²¹ is a singlebond, phenylene, —O—R³³—, or —C(═O)—Y—R³³— wherein Y is oxygen or NH andR³³ is a straight, branched or cyclic C₁-C₆ alkylene group, alkenylenegroup or phenylene group, which may contain a carbonyl (—CO—), ester(—COO—), ether (—O—) or hydroxyl radical. R²², R²³, R²⁵, R²⁶, R²⁷, R²⁹,R³⁰, and R³¹ are each independently a straight, branched or cyclicC₁-C₁₂ alkyl group which may contain a carbonyl, ester or ether radical,or a C₆-C₁₂ aryl group, C₇-C₂₀ aralkyl group, or thiophenyl group. Z₀ isa single bond, methylene, ethylene, phenylene, fluorinated phenylene,—O—R³²—, or —C(═O)—Z₁—R³²— wherein Z₁ is oxygen or NH and R² is astraight, branched or cyclic C₁-C₆ alkylene group, alkenylene group orphenylene group, which may contain a carbonyl, ester, ether or hydroxylradical. M is a non-nucleophilic counter ion.

In addition to the foregoing units, the base polymer (B) may furthercomprise recurring units derived from carbon-to-carbon doublebond-bearing monomers other than the above-described ones, for example,substituted acrylic acid esters such as methyl methacrylate, methylcrotonate, dimethyl maleate and dimethyl itaconate, unsaturatedcarboxylic acids such as maleic acid, fumaric acid, and itaconic acid,cyclic olefins such as norbornene, norbornene derivatives, andtetracyclo[4.4.0.1^(2,5).1^(7,10)]dodecene derivatives, unsaturated acidanhydrides such as itaconic anhydride, and other monomers.

In the resist composition, (C) an acid generator, typically photoacidgenerator (PAG) is compounded. The PAG may be any compound capable ofgenerating an acid upon exposure of high-energy radiation. Suitable PAGsinclude sulfonium salts, iodonium salts, sulfonyldiazomethane,N-sulfonyloxyimide, and oxime-O-sulfonate acid generators. Exemplaryacid generators are described in US 20090274978 (JP-A 2009-269953,paragraphs [0151] to [0156]).

The preferred PAGs are those compounds of the general formula (C)-1.

Herein R⁴⁰⁵, R⁴⁰⁶, and R⁴⁰⁷ are each independently hydrogen or astraight, branched or cyclic C₁-C₂₀ monovalent hydrocarbon group whichmay contain a heteroatom, typically an alkyl or alkoxy group. R⁴⁰⁸ is astraight, branched or cyclic C₇-C₃₀ monovalent hydrocarbon group whichmay contain a heteroatom.

Examples of the hydrocarbon groups optionally containing a heteroatom,represented by R⁴⁰⁵, R⁴⁰⁶, and R⁴⁰⁷, include methyl, ethyl, propyl,isopropyl, n-butyl, sec-butyl, tert-butyl, tert-amyl, n-pentyl, n-hexyl,cyclopentyl, cyclohexyl, ethylcyclopentyl, butylcyclopentyl,ethylcyclohexyl, butylcyclohexyl, adamantyl, ethyladamantyl,butyladamantyl, and modified forms of the foregoing in which anycarbon-carbon bond is separated by a hetero-atomic grouping such as —O—,—S—, —SO—, —SO₂—, —NH—, —C(═O)—, —C(═O)O—, or —C(═O)NH—, or any hydrogenatom is replaced by a functional group such as —OH, —NH, —CHO, or —CO₂H.Examples of the straight, branched or cyclic C₇-C₃₀ monovalenthydrocarbon groups optionally containing a heteroatom, represented byR⁴⁰⁸, are shown below, but not limited thereto.

Illustrative examples of acid generator (C)-1 are shown below, but notlimited thereto.

It is noted that an acid diffusion controlling function may be providedwhen two or more PAGs are used in admixture provided that one PAG is anonium salt capable of generating a weak acid. Specifically, in a systemusing a mixture of a PAG capable of generating a strong acid (e.g.,fluorinated sulfonic acid) and an onium salt capable of generating aweak acid (e.g., non-fluorinated sulfonic acid or carboxylic acid), ifthe strong acid generated by the PAG upon exposure to high-energyradiation collides with the unreacted onium salt having a weak acidanion, then a salt exchange occurs whereby the weak acid is released andan onium salt having a strong acid anion is formed. In this course, thestrong acid is exchanged into the weak acid having a low catalysis,incurring apparent deactivation of the acid for enabling to control aciddiffusion.

If the PAG capable of generating a strong acid is also an onium salt, anexchange from the strong acid (generated upon exposure to high-energyradiation) to a weak acid as above can take place, but it never happensthat the weak acid (generated upon exposure to high-energy radiation)collides with the unreacted onium salt capable of generating a strongacid to induce a salt exchange. This is because of a likelihood of anonium cation forming an ion pair with a stronger acid anion.

An appropriate amount of PAG added is 0.1 to 40 parts, and morepreferably 0.1 to 20 parts by weight per 100 parts by weight of the baseresin (B) in the composition. As long as PAG is up to 40 phr, theresulting resist film has a fully high transmittance and a minimallikelihood of degraded resolution. The PAG may be used alone or inadmixture of two or more. The transmittance of the resist film can becontrolled by using a PAG having a low transmittance at the exposurewavelength and adjusting the amount of the PAG added.

The resist composition may further comprise one or more of (D) anorganic solvent, (E) a basic compound, (F) a dissolution regulator, (G)a surfactant, and (H) an acetylene alcohol derivative.

The organic solvent (D) used herein may be any organic solvent in whichpolymer P1, the base resin, PAG, and other components are soluble.Exemplary solvents are described in JP-A 2008-111103, paragraph [0144].The organic solvents may be used alone or in combinations of two or morethereof. An appropriate amount of the organic solvent used is 200 to10,000 parts, especially 400 to 7,000 parts by weight per 100 parts byweight of the base resin (B). It is recommended to use diethylene glycoldimethyl ether, 1-ethoxy-2-propanol, propylene glycol monomethyl etheracetate (PGMEA), and mixtures thereof because the acid generator is mostsoluble therein.

As the basic compound (E), nitrogen-containing organic compounds arepreferred and may be used alone or in admixture. Those compounds capableof suppressing the rate of diffusion when the acid generated by the PAGdiffuses within the resist film are useful. The inclusion of suchquencher facilitates adjustment of resist sensitivity and holds down therate of acid diffusion within the resist film, resulting in betterresolution. In addition, it suppresses changes in sensitivity followingexposure and mitigates substrate poisoning and environment dependence,as well as improving the exposure latitude and the pattern profile.

Suitable nitrogen-containing organic compounds include primary,secondary, and tertiary aliphatic amines, mixed amines, aromatic amines,heterocyclic amines, nitrogen-containing compounds having carboxylgroup, nitrogen-containing compounds having sulfonyl group,nitrogen-containing compounds having hydroxyl group, nitrogen-containingcompounds having hydroxyphenyl group, alcoholic nitrogen-containingcompounds, amide, imide and carbamate derivatives. Illustrative examplesare described in JP-A 2009-269953, paragraphs [0122] to [0141].

The basic compound is preferably used in an amount of 0.001 to 8 parts,more preferably 0.01 to 4 parts by weight per 100 parts by weight of thebase resin (B). Less than 0.001 phr fails to achieve the desiredaddition effect whereas more than 8 phr may lead to a lowering ofsensitivity. The preferred nitrogen-containing organic compound is acompound capable of holding down the diffusion rate of acid when theacid generated by the acid generator diffuses in the resist film. Theinclusion of the nitrogen-containing organic compound holds down thediffusion rate of acid in the resist film, which leads to manyadvantages including improved resolution, minimized sensitivity changefollowing exposure, reduced substrate poisoning and environmentdependency, and improved exposure latitude and pattern profile.

The dissolution regulator or inhibitor (F) which can be added to theresist composition is a compound having on the molecule at least twophenolic hydroxyl groups which are protected with an acid labile group,or a compound having on the molecule at least one carboxyl group whichis protected with an acid labile group. Exemplary regulators aredescribed in JP-A 2008-122932, paragraphs [0155] to [0178]. Thedissolution regulator is preferably used in an amount of 0 to 40 parts,more preferably 5 to 30 parts by weight per 100 parts by weight of thebase resin (B).

Optionally, the resist composition may further comprise (G) a surfactantwhich is commonly used for facilitating the coating operation. Exemplarysurfactants are described in JP-A 2008-111103, paragraph [0166].

Optionally, the resist composition may further comprise (H) an acetylenealcohol derivative. Exemplary compounds are described in JP-A2008-122932, paragraphs [0180] to [0181].

Optionally, the resist composition may further comprise (I) afluorinated alcohol. When the resist composition contains (E) a basiccompound, the fluorinated ester in recurring units (1a) of polymer P1 issubject to gradual hydrolysis during shelf storage, which may lead to adecline of water repellent and water slip performance during theimmersion lithography process. In such a case, (I) a fluorinated alcoholmay be added to the resist composition for suppressing the hydrolysiswhich is otherwise promoted by the basic compound (E), thus enhancingstorage stability. Examples of the fluorinated alcohol include, but arenot limited to, 2,2,2-trifluoroethanol, 2,2,3,3-tetrafluoro-1-propanol,1,3-difluoro-2-propanol, 1,1,1,3,3,3-hexafluoro-2-propanol,1,1,1,3,3,3-hexafluoro-2-trifluoromethyl-2-propanol,2,2,3,4,4,4-hexafluoro-1-butanol, 2,2,2,2′,2′,2′-hexafluorocumylalcohol,and 2,2,3,3,4,4,5,5-octafluoro-1-pentanol. The fluorinated alcohol (I)is preferably used in an amount of 0.01 to 10 parts, more preferably0.01 to 5 parts by weight per part by weight of the basic compound (E).

Pattern Forming Process

It is now described how to form a pattern using the resist compositionof the invention. A pattern may be formed from the resist compositionusing any well-known lithography process. The preferred process includesat least the steps of forming a resist film on a substrate, exposing itto high-energy radiation, and developing it with a developer.

The resist composition is applied onto a substrate, typically a siliconwafer by a suitable coating technique such as spin coating. The coatingis prebaked on a hot plate at a temperature of 60 to 150° C. for 1 to 10minutes, preferably 80 to 140° C. for 1 to 5 minutes, to form a resistfilm of 0.01 to 2.0 μm thick. It is noted in conjunction with spincoating that if the resist composition is coated onto the surface of asubstrate which has been wetted with the resist solvent or a solutionmiscible with the resist solvent, then the amount of the resistcomposition dispensed can be reduced (see JP-A H09-246173).

A mask having the desired pattern is then placed over the resist film,and the film exposed through the mask to an electron beam or tohigh-energy radiation such as deep-UV, excimer laser or x-ray in a doseof 1 to 200 mJ/cm², and preferably 10 to 100 mJ/cm². The high-energyradiation used herein preferably has a wavelength in the range of 180 to250 nm.

Light exposure may be dry exposure in air or nitrogen atmosphere, orimmersion lithography of providing a liquid, typically water between theresist film and the projection lens. The liquid used for immersion is aliquid having a refractive index of at least 1 and high transparency atthe exposure wavelength, such as water or alkane. EB or EUV exposure invacuum is also acceptable.

The resist film formed from the resist composition has such barrierproperties against water that it may inhibit resist components frombeing leached out in water and as a consequence, eliminate a need for aprotective coating in the immersion lithography and reduce the costassociated with protective coating formation and removal. The resistfilm has so high a receding contact angle with water that few liquiddroplets may be left on the surface of the resist film after immersionlithography scanning, minimizing pattern formation failures induced byliquid droplets left on the film surface.

In another version of immersion lithography, a protective coating may beformed on top of the resist film. The resist protective coating may beeither of the solvent stripping type or of the developer dissolutiontype. A resist protective coating of the developer dissolution type isadvantageous for process simplicity because it can be stripped duringdevelopment of a resist film. The resist protective coating used in theimmersion lithography may be formed from a coating solution, forexample, a topcoat solution of a polymer having acidic units such as1,1,1,3,3,3-hexafluoro-2-hydroxy-2-propyl, carboxyl or sulfo groupswhich is insoluble in water and soluble in an alkaline developer liquid,in a solvent selected from alcohols of at least 4 carbon atoms, ethersof 8 to 12 carbon atoms, and mixtures thereof. The resist protectivecoating is not limited thereto.

The resist protective coating may be formed by spin coating a topcoatsolution onto a prebaked resist film, and prebaking on a hot plate at 50to 150° C. for 1 to 10 minutes, preferably at 70 to 140° C. for 1 to 5minutes. Preferably the protective coating has a thickness in the rangeof 10 to 500 nm. As in the case of resist compositions, the amount ofthe protective coating material dispensed in forming a protectivecoating by spin coating may be reduced by previously wetting the resistfilm surface with a suitable solvent and applying the protective coatingmaterial thereto.

After exposure to high-energy radiation through a photomask, the resistfilm is baked (PEB) on a hot plate at 60 to 150° C. for 1 to 5 minutes,and preferably at 80 to 140° C. for 1 to 3 minutes.

Where a resist protective coating is used, sometimes water is left onthe protective coating prior to PEB. If PEB is performed in the presenceof residual water, water can penetrate through the protective coating tosuck up the acid in the resist during PEB, impeding pattern formation.To fully remove the water on the protective coating prior to PEB, thewater on the protective coating should be dried or recovered by suitablemeans, for example, spin drying, purging the protective coating surfacewith dry air or nitrogen, or optimizing the shape of a water recoverynozzle on the relevant stage or a water recovery process.

After the exposure, development is carried out by a conventional methodsuch as dip, puddle, or spray development with an aqueous alkalinesolution such as tetramethylammonium hydroxide (TMAH) solution. Thedeveloper may have a concentration of 0.1 to 5 wt %, preferably 2 to 3wt %. A typical developer is a 2.38 wt % TMAH aqueous solution. Thedevelopment time is 10 to 300 seconds, and preferably 0.5 to 2 minutes.These steps result in the formation of the desired pattern on thesubstrate.

Where polymer P1 is used as an additive to a resist material for usewith mask blanks, a resist solution is prepared by adding polymer P1 toa base resin and dissolving them in an organic solvent. The resistsolution is coated on a mask blank substrate of SiO₂, Cr, CrO, CrN, MoSior the like. A SOG film and an organic undercoat film may intervenebetween the resist film and the blank substrate to construct athree-layer structure which is also acceptable herein.

As the base resin of the resist composition for use with mask blanks,novolac resins and hydroxystyrene are often used. Those resins in whichalkali soluble hydroxyl groups are substituted by acid labile groups areused for positive resists while these resins in combination withcrosslinking agents are used for negative resists. Base polymers whichcan be used herein include copolymers of hydroxystyrene with one or moreof (meth)acrylic derivatives, styrene, vinylnaphthalene,vinylanthracene, vinylpyrene, hydroxyvinylnaphthalene,hydroxyvinylanthracene, indene, hydroxyindene, acenaphthylene, andnorbornadiene derivatives.

Once the resist film is formed, the structure is exposed to EB in vacuumusing an EB image-writing system. The exposure is followed by baking(PEB) and development in an alkaline developer for 10 to 300 seconds,thereby forming a pattern.

Example

Examples are given below by way of illustration and not by way oflimitation. The abbreviations Mw and Mn are weight and number averagemolecular weights, respectively, as measured versus polystyrenestandards by gel permeation chromatography (GPC) using tetrahydrofuranas solvent, and Mw/Mn is a polydispersity index.

Polymer Synthesis Synthesis Example 1-1 Synthesis of Polymer 1

In a nitrogen atmosphere, a flask was charged with 15.0 g of ethyleneglycol methacrylate[3,3,3-trifluoro-2-hydroxy-2-(trifluoromethyl)propionate], 0.53 g ofdimethyl 2,2′-azobis(isobutyrate), and 15.0 g of methyl ethyl ketone toform a monomer solution at a temperature of 20-25° C. In a nitrogenatmosphere, another flask was charged with 7.50 g of methyl ethylketone, which was heated at 80° C. with stirring. The monomer solutionwas added dropwise thereto over 4 hours. After the completion ofdropwise addition, the polymerization solution was stirred for a further2 hours while maintaining the temperature of 80° C. At the end ofmaturing, the solution was cooled to room temperature. Thepolymerization solution was transferred to an eggplant-shape flask andconcentrated using an evaporator. Then toluene was added to the flask soas to eventually form a 40 wt % solution of toluene/methyl ethyl ketone(mix ratio 9/1). The solution was added dropwise to 150 g of hexanewhereupon a copolymer precipitated. The copolymer was collected byfiltration, washed with 90 g of hexane, and separated as a white solid.The white solid was vacuum dried at 50° C. for 20 hours, yielding thetarget polymer, designated Polymer 1, in white powder solid form. Amount12.7 g, yield 80%.

Synthesis Examples 1-2 to 1-22 and Comparative Synthesis Examples 1-1 to1-3 Synthesis of Polymers 2 to 22 and Comparative Polymers 1 to 3

Polymers 2 to 22 and Comparative Polymers 1 to 3 were synthesized as inSynthesis Example 1-1 aside from changing the amount and type ofmonomers. It is noted that the values of c, d, e and f are molar ratiosof monomer units.

Preparation of Resist Examples 1-1 to 1-30 and Comparative Examples 1-1to 1-4

A resist solution was prepared by combining an additive polymer(Polymers 1 to 22 and Comparative Polymers 1 to 3), a base resin (ResistPolymers 1 and 2), an acid generator, a basic compound, and a solvent inaccordance with the formulation shown in Table 1, mixing and dissolvingthe components, and filtering through a Teflon® filter having a poresize of 0.2 μm. The solvent contained 0.01 wt % of a surfactant KH-20(Asahi Chemical Industry Co., Ltd.). In this way, inventive resistcompositions R-01 to R-30 and comparative resist compositions R-31 toR-34 were obtained.

TABLE 1 Additive polymer Base resin PAG Base Solvent 1 Solvent 2 Resist(pbw) (pbw) (pbw) (pbw) (pbw) (pbw) Example 1-1 R-01 Polymer 1 ResistPolymer 1 PAG1 Base1 PGMEA CyHO (5.0) (80) (15.0) (4.0) (2,700) (300)1-2 R-02 Polymer 2 Resist Polymer 1 PAG1 Base1 PGMEA CyHO (5.0) (80)(15.0) (4.0) (2,700) (300) 1-3 R-03 Polymer 3 Resist Polymer 1 PAG1Base1 PGMEA CyHO (5.0) (80) (15.0) (4.0) (2,700) (300) 1-4 R-04 Polymer4 Resist Polymer 1 PAG1 Base1 PGMEA CyHO (5.0) (80) (15.0) (4.0) (2,700)(300) 1-5 R-05 Polymer 5 Resist Polymer 1 PAG1 Base1 PGMEA CyHO (5.0)(80) (15.0) (4.0) (2,700) (300) 1-6 R-06 Polymer 6 Resist Polymer 1 PAG1Base1 PGMEA CyHO (5.0) (80) (15.0) (4.0) (2,700) (300) 1-7 R-07 Polymer7 Resist Polymer 1 PAG1 Base1 PGMEA CyHO (5.0) (80) (15.0) (4.0) (2,700)(300) 1-8 R-08 Polymer 8 Resist Polymer 1 PAG1 Base1 PGMEA CyHO (5.0)(80) (15.0) (4.0) (2,700) (300) 1-9 R-09 Polymer 9 Resist Polymer 1 PAG1Base1 PGMEA CyHO (5.0) (80) (15.0) (4.0) (2,700) (300) 1-10 R-10 Polymer10 Resist Polymer 1 PAG1 Base1 PGMEA CyHO (5.0) (80) (15.0) (4.0)(2,700) (300) 1-11 R-11 Polymer 11 Resist Polymer 1 PAG1 Base1 PGMEACyHO (5.0) (80) (15.0) (4.0) (2,700) (300) 1-12 R-12 Polymer 12 ResistPolymer 1 PAG1 Base1 PGMEA CyHO (5.0) (80) (15.0) (4.0) (2,700) (300)1-13 R-13 Polymer 13 Resist Polymer 1 PAG1 Base1 PGMEA CyHO (5.0) (80)(15.0) (4.0) (2,700) (300) 1-14 R-14 Polymer 14 Resist Polymer 1 PAG1Base1 PGMEA CyHO (5.0) (80) (15.0) (4.0) (2,700) (300) 1-15 R-15 Polymer15 Resist Polymer 1 PAG1 Base1 PGMEA CyHO (5.0) (80) (15.0) (4.0)(2,700) (300) 1-16 R-16 Polymer 16 Resist Polymer 1 PAG1 Base1 PGMEACyHO (5.0) (80) (15.0) (4.0) (2,700) (300) 1-17 R-17 Polymer 17 ResistPolymer 1 PAG1 Base1 PGMEA CyHO (5.0) (80) (15.0) (4.0) (2,700) (300)1-18 R-18 Polymer 18 Resist Polymer 1 PAG1 Base1 PGMEA CyHO (5.0) (80)(15.0) (4.0) (2,700) (300) 1-19 R-19 Polymer 19 Resist Polymer 1 PAG1Base1 PGMEA CyHO (5.0) (80) (15.0) (4.0) (2,700) (300) 1-20 R-20 Polymer20 Resist Polymer 1 PAG1 Base1 PGMEA CyHO (5.0) (80) (15.0) (4.0)(2,700) (300) 1-21 R-21 Polymer 21 Resist Polymer 1 PAG1 Base1 PGMEACyHO (5.0) (80) (15.0) (4.0) (2,700) (300) 1-22 R-22 Polymer 22 ResistPolymer 1 PAG1 Base1 PGMEA CyHO (5.0) (80) (15.0) (4.0) (2,700) (300)1-23 R-23 Polymer 7 Resist Polymer 1 PAG2 Base1 PGMEA CyHO (5.0) (80)(15.0) (4.0) (2,700) (300) 1-24 R-24 Polymer 8 Resist Polymer 1 PAG2Base2 PGMEA CyHO (5.0) (80) (15.0) (4.0) (2,700) (300) 1-25 R-25 Polymer13 Resist Polymer 1 PAG2 Base1 PGMEA CyHO (5.0) (80) (15.0) (4.0)(2,700) (300) 1-26 R-26 Polymer 18 Resist Polymer 1 PAG2 Base1 PGMEACyHO (5.0) (80) (15.0) (4.0) (2,700) (300) 1-27 R-27 Polymer 7 ResistPolymer 2 Base1 PGMEA GBL (5.0) (80) (4.0) (2,700) (300) 1-28 R-28Polymer 8 Resist Polymer 2 Base1 PGMEA GBL (5.0) (80) (4.0) (2,700)(300) 1-29 R-29 Polymer 13 Resist Polymer 2 Base1 PGMEA GBL (5.0) (80)(4.0) (2,700) (300) 1-30 R-30 Polymer 18 Resist Polymer 2 Base1 PGMEAGBL (5.0) (80) (4.0) (2,700) (300) Comparative 1-1 R-31 ComparativePolymer 1 Resist Polymer 1 PAG1 Base1 PGMEA CyHO Example (5.0) (80)(15.0) (4.0) (2,700) (300) 1-2 R-32 Comparative Polymer 2 Resist Polymer1 PAG1 Base1 PGMEA CyHO (5.0) (80) (15.0) (4.0) (2,700) (300) 1-3 R-33Comparative Polymer 3 Resist Polymer 1 PAG1 Base1 PGMEA CyHO (5.0) (80)(15.0) (4.0) (2,700) (300) 1-4 R-34 Resist Polymer 1 PAG1 Base1 PGMEACyHO (80) (15.0) (4.0) (2,700) (300)

The abbreviations for acid generator, base and solvent in Table 1 areidentified below.

Resist Evaluation Examples 2-1 to 2-30 and Comparative Examples 2-1 to2-4

An antireflective coating ARC-29A (Nissan Chemical Co., Ltd.) wasdeposited on a silicon substrate to a thickness of 87 nm. The resistsolution was applied onto the ARC and baked at 120° C. for 60 seconds toform a resist film of 150 nm thick.

A contact angle with water of the resist film was measured, using aninclination contact angle meter Drop Master 500 by Kyowa InterfaceScience Co., Ltd. Specifically, the wafer covered with the resist filmwas kept horizontal, and 50 μL of pure water was dropped on the resistfilm to form a droplet. While the wafer was gradually inclined, theangle (sliding angle) at which the droplet started sliding down wasdetermined as well as receding contact angle. The results are shown inTable 2.

A smaller sliding angle indicates an easier flow of water on the resistfilm. A larger receding contact angle indicates that fewer liquiddroplets are left during high-speed scan exposure. It is demonstrated inTable 2 that the inclusion of the additive polymer of the invention in aresist solution achieves a drastic improvement in the receding contactangle of resist film without adversely affecting the sliding angle, ascompared with those resist films free of the additive polymer.

Also, the resist film-bearing wafer (prepared above) was irradiatedthrough an open frame at an energy dose of 50 mJ/cm² using an ArFscanner S305B (Nikon Corp.). Then a true circle ring of Teflon® havingan inner diameter of 10 cm was placed on the resist film, 10 mL of purewater was carefully injected inside the ring, and the resist film waskept in contact with water at room temperature for 60 seconds.Thereafter, the water was recovered, and a concentration of photoacidgenerator (PAG1) anion in the water was measured by an LC-MS analyzer(Agilent). The results are also shown in Table 2.

It is evident from Table 2 that a resist film formed from a resistsolution containing the additive polymer according to the invention iseffective in inhibiting the PAG from being leached out of the film inwater.

Further, the resist film-bearing wafer (prepared above) was exposed bymeans of an ArF scanner model S307E (Nikon Corp., NA 0.85, σ 0.93, 4/5annular illumination, 6% halftone phase shift mask), rinsed for 5minutes while splashing pure water, baked (PEB) at 110° C. for 60seconds, and developed with a 2.38 wt % TMAH aqueous solution for 60seconds, forming a 75-nm line-and-space pattern. The wafer wassectioned, and the profile and sensitivity of the 75-nm line-and-spacepattern were evaluated. The results are also shown in Table 2.

As seen from Table 2, when exposure is followed by water rinsing, theresist film having the additive polymer according to the inventionformulated therein formed a pattern of rectangular profile, in starkcontrast with the resist film free of the additive polymer forming apattern of T-top profile.

TABLE 2 Receding Sliding contact Anion 75-nm angle angle Leach-outSensitivity pattern Resist (°) (°) (ppb) (mJ/cm²) profile Example 2-1R-01 16 69 8 31 rectangular 2-2 R-02 12 75 7 31 rectangular 2-3 R-03 1769 8 31 rectangular 2-4 R-04 11 75 6 31 rectangular 2-5 R-05 8 81 6 31rectangular 2-6 R-06 7 80 6 31 rectangular 2-7 R-07 11 76 7 31rectangular 2-8 R-08 10 80 6 31 rectangular 2-9 R-09 11 78 7 31rectangular 2-10 R-10 13 77 7 30 rectangular 2-11 R-11 7 81 6 31rectangular 2-12 R-12 10 79 6 31 rectangular 2-13 R-13 9 81 6 31rectangular 2-14 R-14 9 80 6 31 rectangular 2-15 R-15 10 80 6 30rectangular 2-16 R-16 9 80 6 31 rectangular 2-17 R-17 8 80 7 30rectangular 2-18 R-18 7 82 6 31 rectangular 2-19 R-19 9 81 6 31rectangular 2-20 R-20 7 83 6 31 rectangular 2-21 R-21 9 79 6 31rectangular 2-22 R-22 10 80 7 30 rectangular 2-23 R-23 11 76 8 29rectangular 2-24 R-24 10 80 7 29 rectangular 2-25 R-25 8 83 7 30rectangular 2-26 R-26 7 82 7 30 rectangular 2-27 R-27 10 77 not detected27 rectangular 2-28 R-28 9 81 not detected 27 rectangular 2-29 R-29 7 84not detected 28 rectangular 2-30 R-30 7 83 not detected 28 rectangularComparative 2-1 R-31 21 62 9 31 rectangular Example 2-2 R-32 19 66 9 33rectangular 2-3 R-33 20 71 9 33 rectangular 2-4 R-34 28 40 60  31 T-top

Evaluation of Resist Pattern Defects Examples 3-1 to 3-6 and ComparativeExamples 3-1 to 3-2

An antireflective coating ARC-29A (Nissan Chemical Co., Ltd.) of 95 nmthick was deposited on a silicon substrate. The resist solution wasapplied onto the ARC and baked at 120° C. for 60 seconds to form aresist film of 150 nm thick. Using an ArF scanner model S610C (NikonCorp., NA 1.20, a 0.98, 4/5 dipole illumination (open angle 35°), binarymask), the resist film on the wafer was exposed at a scan speed of 500mm/s. This was followed by baking (PEB) at 110° C. for 60 seconds anddevelopment with a 2.38 wt % TMAH aqueous solution for 30 seconds. Thewafer as developed was further baked at 110° C. for 60 seconds,completing a 45-nm line-and-space pattern.

Using a flaw detector, the number of defects on the pattern was counted.The pattern was observed under scanning electron microscope (SEM) to seewhether the defects were bridge defects or watermark defects. The“bridge defect” is formed by the mechanism that foreign matter depositsin a space to form a bridge between adjacent lines. The “watermarkdefect” is characterized in that the pattern is waved and the wavedportion covers several lines in a circular fashion. It is believed thatthe watermark defect is caused by a residual water droplet from theimmersion water. The watermark defect tends to form when the resist filmsurface is short of water repellency.

FIGS. 1 and 2 are SEM images of bridge defect and watermark defect,respectively. The counts of bridge defects and watermark defects arereported in Table 3.

TABLE 3 Bridge defects Watermark defects Resist (count) (count) Example3-1 R-06 8 9 3-2 R-07 5 3 3-3 R-08 2 2 3-4 R-23 3 2 3-5 R-27 3 5 3-6R-28 2 3 Comparative 3-1 R-31 9 33 Example 3-2 R-32 25 21

It is evident from Table 3 that the resist compositions within the scopeof the invention are effective for reducing both bridge defects andwatermark defects since the resist compositions take full advantage ofthe additive polymer according to the invention featuring a satisfactoryalkali dissolution rate and a high receding contact angle.

Japanese Patent Application No. 2010-277875 is incorporated herein byreference.

Although some preferred embodiments have been described, manymodifications and variations may be made thereto in light of the aboveteachings. It is therefore to be understood that the invention may bepracticed otherwise than as specifically described without departingfrom the scope of the appended claims.

The invention claimed is:
 1. A resist composition comprising (A) apolymer comprising recurring units of the following general formula(1a), (B) a polymer having a lactone ring-deviated structure,hydroxyl-containing structure and/or maleic anhydride-derived structureand adapted to become soluble in an alkaline developer under the actionof an acid as a base resin, (C) a compound capable of generating an acidupon exposure to high-energy radiation, and (D) an organic solvent,

wherein R¹ is hydrogen, R² is hydrogen or methyl, Aa is a branchedC₂-C₂₀ hydrocarbon group having a valence of k¹+1 selected from thegroup consisting of the following groups:

wherein the broken line designates a valence bond, Ab is a straight,branched or cyclic C₁-C₆ divalent hydrocarbon group, k¹ is an integer of1 to 3, and k² is 0 or
 1. 2. The resist composition of claim 1comprising (A) a polymer comprising recurring units of the generalformula (1a) as set forth in claim 1 and recurring units of one or moretype selected from the general formulae (2a) to (2j), (B) a polymerhaving a lactone ring-derived structure, hydroxyl-containing structureand/or maleic anhydride-derived structure and adapted to become solublein alkaline developer under the action of acid as a base resin, (C) acompound capable of generating an acid upon exposure to high-energyradiation, and (D) an organic solvent,

wherein R² is as defined above, R^(4a) and R^(4b) are each independentlyhydrogen or a straight, branched or cyclic C₁-C₁₅ monovalent hydrocarbongroup, or R^(4a) and R^(4b) may bond together to form a non-aromaticring of 3 to 8 carbon atoms with the carbon atom to which they areattached, R^(5a) is hydrogen, a straight, branched or cyclic C₁-C₁₅monovalent hydrocarbon or fluorinated hydrocarbon group, or an acidlabile group, in the case of hydrocarbon group, a constituent moiety—CH₂— may be replaced by —O— or —C(═O)—, R^(6a), R^(6b) and R^(6b) andR^(6c) are each independently hydrogen, or a straight, branched orcyclic C₁-C₁₅ monovalent hydrocarbon group, R^(6a) and R^(6b), R^(6a)and R^(6c), or R^(6b) and R^(6c) may bond together to form anon-aromatic ring of 3 to 8 carbon atoms with the carbon atom to whichthey are attached, R^(7a) is hydrogen, or a straight, branched or cyclicC₁-C₁₅ monovalent hydrocarbon group, R^(7b) is a straight, branched orcyclic C₁-C₁₅ monovalent hydrocarbon group, R^(7a) and R^(7b) may bondtogether to form a non-aromatic ring of 3 to 8 carbon atoms with thecarbon atom to which they are attached, R^(8a), R^(8b) and R^(8c) areeach independently a straight, branched or cyclic C₁-C₁₅ monovalentfluorinated hydrocarbon group, R^(9a) is a straight, branched or cyclicC₁-C₁₅ monovalent hydrocarbon or fluorinated hydrocarbon group, and k²is 0 or
 1. 3. The resist composition of claim 1 wherein the polymer (B)is selected from the group consisting of (meth)acrylate polymers,(α-trifluoromethyl)acrylate-maleic anhydride copolymers,cycloolefin-maleic anhydride copolymers, polynorbornene, polymersresulting from ring-opening metathesis polymerization of cycloolefins,hydrogenated polymers resulting from ring-opening metathesispolymerization of cycloolefins, copolymers of hydroxystyrene with(meth)acrylate, styrene, vinylnaphthalene, vinylanthracene, vinylpyrene,hydroxyvinylnaphthalene, hydroxyvinylanthracene, indene, hydroxyindene,acenaphthylene, or norbornadiene derivatives, and novolac resins.
 4. Theresist composition of claim 1 wherein the polymer (B) further comprisesrecurring units of at least one type selected from the general formulae(2A) to (2D):

wherein R^(1A) is hydrogen, fluorine, methyl or trifluoromethyl, XA isan acid labile group, XB and XC are each independently a single bond ora straight or branched C₁-C₄ divalent hydrocarbon group, YA is asubstituent group having a lactone structure, ZA is hydrogen, a C₁-C₁₅fluoroalkyl group or C₁-C₁₅ fluoroalcohol-containing substituent group,and k^(1A) is an integer of 1 to
 3. 5. The resist composition of claim 1wherein the polymer (A) comprising recurring units of formula (1a) isadded in an amount of 0.1 to 50 parts by weight per 100 parts by weightof the polymer (B).
 6. The resist composition of claim 1, furthercomprising (E) a basic compound.
 7. The resist composition of claim 1,further comprising (F) a dissolution regulator.
 8. A pattern formingprocess comprising the steps of (1) applying the resist composition ofclaim 1 onto a substrate, (2) heat treating and exposing the resultingresist film to high-energy radiation through a photomask, and (3)developing with a developer.
 9. A pattern forming process comprising thesteps of (1) applying the resist composition of claim 1 onto asubstrate, (2) heat treating and exposing the resulting resist film tohigh-energy radiation from a projection lens through a photomask whileholding a liquid between the substrate and the projection lens, and (3)developing with a developer.
 10. A pattern forming process comprisingthe steps of (1) applying the resist composition of claim 1 onto asubstrate to form a resist film, (2) forming a protective coating ontothe resist film, (3) heat treating and exposing the resist film tohigh-energy radiation from a projection lens through a photomask whileholding a liquid between the substrate and the projection lens, and (4)developing with a developer.
 11. The process of claim 9 wherein theliquid is water.
 12. The process of claim 8 wherein the high-energyradiation has a wavelength in the range of 180 to 250 nm.
 13. A patternforming process comprising the steps of (1) applying the resistcomposition of claim 1 onto a mask blank, (2) heat treating and exposingthe resulting resist film in vacuum to electron beam, and (3) developingwith a developer.
 14. A resist composition comprising (A) a polymercomprising recurring units of the general formula (1a) and recurringunits of one or more type selected from the general formulae (2c), (2d),(2g), (2h), (2i) and (2j), (B) a polymer having a lactone ring-derivedstructure, hydroxyl-containing structure and/or maleic anhydride-derivedstructure and adapted to become soluble in an alkaline developer underthe action of acid as a base resin, (C) a compound capable of generatingan acid upon exposure to high-energy radiation, and (D) an organicsolvent,

wherein R¹ is hydrogen, R² is hydrogen or methyl, Aa is a straight orbranched C₁-C₂₀ hydrocarbon group having a valence of k¹⁺¹, Ab is astraight, branched or cyclic C₁-C₆ divalent hydrocarbon group, k¹ is aninteger of 1 to 3, and k² is 0 or 1,

wherein R² is as defined above, R^(4a) and R^(4b) are each independentlyhydrogen or a straight, branched or cyclic C₁-C₁₅ monovalent hydrocarbongroup, or R^(4a) and R^(4b) may bond together to form a non-aromaticring of 3 to 8 carbon atoms with the carbon atom to which they areattached, one of R^(6a), R^(6b) and R^(6c) is hydrogen, or a straight,branched or cyclic C₁-C₁₅ monovalent hydrocarbon group, the remainingR^(6a) and R^(6b), R^(6a) and R^(6c), or R^(6b) and R^(6c) bond togetherto form a non-aromatic ring of 3 to 8 carbon atoms with the carbon atomto which they are attached, R^(7a) is hydrogen, or a straight, branchedor cyclic C₁-C₁₅ monovalent hydrocarbon group, R^(7b) is a straight,branched or cyclic C₁-C₁₅ monovalent hydrocarbon group, R^(8a), R^(8b)and R^(8c) are each independently a straight, branched or cyclic C₁-C₁₅monovalent fluorinated hydrocarbon group, R^(9a) is a straight, branchedor cyclic C₁-C₁₅ monovalent hydrocarbon or fluorinated hydrocarbongroup, and k² is 0 or
 1. 15. The resist composition of claim 14 whereinthe polymer (A) comprising the recurring units of formula (1) and therecurring units of one or more type selected from the general formulae(2g), (2h), (2i) and (2j):

wherein R^(4a), R^(4b), R^(8a), R^(8b), R^(8c), R^(9a) and k² are asdefined above.
 16. The resist composition of claim 14 wherein Aa informula (1a) is selected from the group consisting of the followinggroups:

wherein the broken line designates a valence bond.